A brushcutter of the kind described above is disclosed in British Patent No. 2,054,035. In this brushcutter, the cooling air for the engine is drawn in and expelled at that end of the engine housing at which the guide tube is located. The warm air expelled from the engine housing can constitute an annoyance for the operator of the brushcutter. In addition, the constrained configuration does not permit the mounting of accessory devices in this region.
Air-cooled internal combustion engines often cause problems when starting and in the initial operational phase when the ambient temperature is very low. Icing on the carburetor and on the filter can occur and increased wear occurs because of inadequate lubrication. Accordingly, it has already been suggested that the cooling air flow be controlled in dependence upon the temperature of the engine as disclosed in U.S. Pat. No. 3,245,390 and British Patent No. 782,078. The cooling air flow is guided in a closed loop by means of the usual blower until the engine has warmed sufficiently. A throttle flap is then opened via a thermal controller which releases the heated cooling air to the ambient. In addition, a second throttle flap can be opened at another location of the engine housing in order to draw in fresh air from the ambient.
These arrangements are not usable in an internal combustion engine of a handheld portable tool because they cannot be accommodated in the spatially small engine housings of necessarily constrained configuration. There is no possibility provided for such a thermal control in the tool mentioned above and disclosed in British Patent No. 2,054,035 wherein the cooling air is expelled and drawn in at the same end of the housing.